The elbow is the joint between the humerus in the upper arm and the ulna and radius in the forearm. The joint between the ulna and the humerus consists primarily of a large depression known as the trochlear notch in the proximal end of the ulna which receives the distal end of the humerus, or trochlea. The proximal end of the ulna, which forms the proximal side of the trochlear notch, is called the olecranon. The triceps muscle, which extends the forearm, attaches at its lower end to the olecranon.
One of the most common fractures of the elbow involves the olecranon. In the most typical fracture pattern, the olecranon is severed from the rest of the ulna along the bottom of the trochlear notch. Such fractures are often difficult to treat because the powerful muscles attached to the olecranon tend to pull it away from the rest of the ulna and rotate it around the trochlea. This displacement of the olecranon fragment must be reduced and stabilized to allow the fracture to heal.
Numerous techniques have been developed to reduce and stabilize olecranon fractures. For instance, U.S. Pat. No. 3,716,050 describes a metal plate that is used to secure olecranon fractures. Although such plates can provide effective reduction and stabilization, they are difficult to install because of the extensive dissection required to expose the large section of the ulna where the plate attaches. Moreover, the plate eliminates so much of the load on the bone that decalcification can result, leading to weakness after the plate is removed.
Another common treatment makes use of a lag screw installed through the proximal end of the olecranon and extending into the medullary canal of the ulna. Because the threaded region of a lag screw engages the hard cortical bone surrounding the medullary canal, the screw tightens rather suddenly as it starts to engage the bone. Selecting a screw with the proper length and thread diameter so that the screw threads tighten just as the proper compression is applied to the olecranon fragment is often difficult. Moreover, if the threads have not tightened adequately when the fragment is properly compressed, the screw may gradually back out.
In order to address the problem of sudden tightening that occurs with lag screws extending into the medullary canal, shorter cancellous screws have been tried for treatment of olecranon fractures. Such screws do not extend into the medullary canal, but rather engage the softer cancellous bone found in the proximal end of the ulna. The soft cancellous bone allows the depth of the screw to be set as necessary to obtain compression of the olecranon fragment without the problem of the screw being too loose or not fitting in far enough. However, because of their length, short screws do not provide adequate resistance to the torque applied to the olecranon as the forearm is extended.
U.S. Pat. No. 3,763,855 describes a device that can be used to repair olecranon fractures and overcomes some of the difficulties of thread engagement presented by lag screws. In particular, a long threaded medullary pin is provided that is fed down the medullary canal of the ulna. The pin threads into a cortical fixation unit that is installed through the side of the ulna distal to the fracture. Because the fixation unit passes through the cortical bone, it is rigidly held in place. However, installation of the device requires holes to be drilled in the bone at two different locations. It can also be difficult to locate the hole in the fixation unit with the end of the pin.
In yet another treatment method, a pair of stiff wires, known as Kirschner wires, are driven through the olecranon into the ulna. The Kirschner wires essentially nail the fracture together. The trailing ends of the wires are bent into U-shaped heads which are driven into the olecranon to capture one end of a tension band. The tension band loops from the proximal end of the olecranon under the ulna and through a hole formed in the ulna on the distal side of the fracture. The tension band keeps the fractured bone segments from separating and the Kirschner wires prevent lateral shifting and torsional rotation. Use of Kirschner wires is a relatively complex procedure and requires a second hole in the bone for the tension band. Moreover, it can be difficult to obtain proper compression with the tension band and the Kirschner wires sometimes back out.
Due to limitations and problems with the existing devices and methods for repair of olecranon fractures, it is an object of the present invention to provide a simple and reliable method and device to treat fractures of the olecranon.
It is another object of the present invention to provide a screw for use in treatment of fractures of the olecranon that does not rely on threads engaged in the bone surrounding the medullary canal.
One more object of the present invention is to provide a method and device for treating olecranon fractures that requires minimal bone access.
Yet another object of the present invention is to provide a method and device for treating olecranon fractures that imparts adequate longitudinal and rotational stability to the olecranon fragment.